(a) Field of the Invention
The present invention relates to a method for controlling transmission power in a cellular system.
(b) Description of the Related Art
A cellular system has a cell structure to efficiently configure a system. FIG. 1 is an exemplified diagram showing a cellular system.
Referring to FIG. 1, in a cellular system, a cell 1 is surrounded by a plurality of cells (Cell 2, Cell 3, Cell 4, Cell 5, Cell 6, and Cell 7). One cell includes a base station (BS) and at least one set of user equipment (UE). In a downlink, a transmitter may be a part of the base station and a receiver may be a part of the user equipment. In an uplink, the transmitter may be a part of the user equipment and the receiver may be a part of the base station.
The cell is an area where one base station provides communication services. A multi-cell may be formed by disposing the base station having at least one cell in plural. The base station that provides the communication services to the user equipment may be referred to a serving base station (Serving BS), and a base station located around the serving base station may be referred to a neighbor base station (Neighbor BS). The cell of the serving base station is referred to as a serving cell, and the cell of the neighbor base station is referred to as a neighbor cell.
In a general cellular system, a plurality of base stations are uniformly disposed and each cell coverage is divided in a hexagonal comb shape. Offline work to dispose the plurality of base stations is performed in consideration of the maximum transmission power of the base station, the user density, the topography, and the maximum capacity of the base station. Any user equipment measures receiving power from the plurality of base stations by using a reference signal, and is connected to the base station having the strongest receiving power. The reference signal is a primary common pilot channel (P-CPICH) signal in, for example, a 3rd generation partnership project (3GPP) system or a preamble signal in a worldwide interoperability for microwave access (WIMAX) system. Each base station transmits the reference signal, including an indicator. The user equipment detects the reference signal to find the base station, and compares the receiving power from the plurality of base stations to select the base station to be connected.
Meanwhile, unlike the general cellular system, a field requiring a system operation that can non-uniformly dispose a plurality of base stations or change the position of the base station has emerged. An example thereof may include a base station (hereinafter referred to as a military base station) in a military tactics communication system. One military base station may be disposed for each troop. Each troop is disposed in a tactical area, and the military base station in charge of each troop may be located in the campsite of the troop. In addition, the position of the military base station may be changed according to the movement of the troop. Therefore, it may be difficult for the military base station to have a uniform disposition like the general cellular system. A wireless mesh network is formed between the military base stations. In addition, the military base station generally includes a global positioning system (GPS) using a satellite to obtain position and time information according to the characteristics of the military system that requires precision measurements.
FIG. 2 is an exemplified diagram showing a cellular system in which a plurality of base stations are non-uniformly disposed.
Referring to FIG. 2, the position of the base station is represented by a dot and a cell coverage is represented by a circle when each base station transmits at the same transmission power. Many areas where coverage is overlapped between the neighbor base stations are generated due to the non-uniform disposition of the base station. In addition, many outage areas are generated between cells. Therefore, the inter-cell interference and path loss according to a distance between the base station and the user equipment may be large. The data rate and the transmission speed can be deteriorate due to the inter-cell interference and the path loss.
Therefore, in the cellular system where the plurality of base stations can be non-uniformly disposed with respect to each other or the position of the base station can be changed, a need exists for a technology that can variably operate the cell coverage.
The above information disclosed in this Background period is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.